In the past, heat-recoverable metal couplings have been developed for joining pipes together for such applications as aircraft hydraulic systems. See for example U.S. Pat. No. 4,135,743, issued Jan. 23, 1979, which is assigned to the assignee of the present invention. As discussed in said patent, couplings have been made entirely out of heat-recoverable metal and are referred to generally as monolithic couplings. Composite couplings have been made using a liner which is driven by heat-recoverable metal to effect sealing. When such a composite pipe coupling having a liner is utilized, the tensile strength characteristics of the coupling itself depend primarily upon the thickness or cross-sectional area of the liner. It can be understood, therefore, that an increase in tensile load strength requires an increase in thickness of the liner and correspondingly a greater driving force to crush the liner with respect to the pipes being coupled. It must be understood that even if the heat-recoverable metal driver portion is unitary it will carry only a nominal amount of tensile load since it is only in frictional contact with the liner. If the driver portion is not unitary, i.e., if it is a plurality of ring segments it would obviously be incapable of carrying any tensile load. Such prior art devices are therefore limited in tensile strength and utility.
The subject composite pipe coupling has been designed for all diameter pipe and especially for large diameter pipe utilized in undersea gas and oil transport. The subject coupling must be capable of withstanding high hydraulic or pneumatic pressure internally and high stresses created by movement of undersea piping by the sea itself during operation. The subject invention provides a composite pipe coupling having a corrosion resistant liner wherein the tensile strength of the composite coupling is not limited by the tensile strength of the lining. The subject invention provides a composite pipe coupling having a pair of tensile rings and complementary external support structure which provide high overall coupling strength independent of liner strength and which both reduces the galvanic corrosion potential and further insures against external contamination.